Plasticizing rubber



Patented Sept. 2, 1952 T "2,609,404 PLASTICIZING RUBBER John J. verbangbwilmingto'n, Del., assignor to E. I. du Pont de Nemours & Company, Wilthing-ton, DeL, a corporation of Delaware olhew ne Appli a n-D ember 3,117,359, y I

Sei fi O- 13 ,062

1 This inventionrelates to a process for plasticizing rubber, novel plasticizing compositions and theresulting plasticized rubber.

It. iswe'll'known thatrubber, when subjected to mechanical working inthe presence of air or oxygen, is rendered more plastic. The degree of plasticization i determined to a large extent. by the time andytemperature ,of milling, When milled for ,a, sufiicient length of time, rubber becomes very soft and at the same time will lose much of its ability to vulcanize. In order to reduce the time of milling and to prevent the deteriorating action of continued milling, it is common practice to add to the rubber, during the milling operation, certain materials which assist in producing a more plastic and workable product. .Materials whichhaye been commonly used are oils, esters, waxes, fats, alcohols, acids, resins and the like which assist. in the production of so t. ruhhen therby .aswel ne act on on the rubber hydrocarbon or by acting as a lubricant. Some of the more common softeners are mineral oil, pine tar, vpalm on, rosin oil, dibutyl phthalate, Pataffinwax, glycerine and stearic acid. Relatively large amounts of these agents must be used to produce the desired softness. The presence of these so-called physical softeners impairs a mnnbereof the'physical properties of the resulting vulcanizate and for this reason their use is undesirable.

Aromatic mercaptans and aromatic mercaptides of divalent heavy metals are now wellknown as chemical plasticizin agents for natural and "synthetic rubbers as disclosed in U, S. Letters "Patents 2,064,580, 2,378,519 and 2,4617 89. Such chemical plasticizing agents soften rubber without requiring the addition of harmful swelling agents and lubricants, such as'oils, which continue 'to-aiTect the physical proper-ties of the rubberafter vulcanization. However, such mercaptans andrnercaptides are relatively expensive and this has somewhat limited their use. M a

' This invention has an an object to provide organic compositions, which, when added in small amounts to rubber during processing, will not,

, '23 Glaims; (Cl. 260-761) on t e rubber, era subs ant ally neut a be materially decr 'qtfi d and Will bev iabo a {ne e iSum t Qn Inave ly, a r lly ecrea etheftine necessary for breakdown of the rubber, but Will also greatly dition -of compounding agents. A further object of this invention is to provide organic chemdecrease the overall :time necessary-for the ad-sicals which, when added 'to rubber, Ewill increase the plasticity of .thenraw product sufiiciently to produce :better zmolding .properties and superior extrusion characteristics. Another object iswto essary. A more specific object is to provide rubr es ici i e c mp,

mer pta Q1.

2 e 1 a ber plasticiai-ng agents having the snow advantages oi the aromatic mercaptans and mercap- -tides ,jbu t which are efiective in smalleramounts'. A still further object is to provide a newand iniproved process fgr plasticizing rubber: Still ot e b t a e 9 Provid w mQPPSiPiQ J of matter and to advancethe art, Still further objects .Will appear hereinafter. V i V T e. abo and oth obie ts a my. h iltipn may be accomplished by mixing into rubber from ab ut -.0 t ab t l- .ty' eie t based on the le ehv o a rubber n a t eizihs ge tlqrf, the group o arom ic mercaptan andarehie ie mercaptides of divalent heavy metals and ;fi a ou 0-00 9 abQL 935% by We sh l phat c .xentheie runner ebie ts 9 mi immanent 9-2 tqabqut hl l Q-nart ci M, ma e merea t nior mercaptide an n 19 the ick lxentha which may be eililp e tures o such i gredients scl itionscfi h Xanth e in the mer p n ri oli t onsofisue two ingredients in a substantially neutral mutual organic solvent, such as a hydrocarbon, alcohol ores er or l nis u es a y wo or :merez hered By he use 9 th nles e z ng omn s tiq 9 invention, rub er can e eelt rel i 1,5- tiizecl to any desired degree whereby the time necessary fer breakdown Q :thez ubberc ndsth e ditien cf com ound i gr dien s q t e i a w i e t e i kel a ha e xehtha esh ve i .c no plasticizing action on rubber Joy th in;

they a e v ry s n p ompt .Q them lq tien of ubber by a ema ie merea tans e c des T us the-use Qf a mal 7 r. V t e me sel alip t c ehthate i h th a einati enereant e so in reajses'the plasticizing action of' the mercaptan and mercaptide that it is possible to obtain a greater plasticizing of the rubber with approximately half the amount of mercaptan that would be used in the absence of the nickel Xanthate. Therefore, it is possible to obtain the desired plasticizing effect on the rubber with materially less amounts of plasticizing agent, particularly mercaptan and mercaptide, resulting in a distinct saving in cost and increasing the usefulness of the aromatic mercaptans and mercaptides.

The aromatic mercaptans and mercaptides may be those known to the art as useful for plasticizing natural and synthetic rubbers and will include aryl mercaptans, aryl polymercaptans and substituted derivatives thereof in which the substituents may be halogen, hydroxyl, nitro, amino, carboxyl, ester and like groups. The aromatic groups may be of the benzene, naphthalene, diphenyl and anthracene series. The aromatic mercaptans and mercaptides have the sulfur directly bonded to a ring carbon atom of a henzene ring. It will usually be preferred to employ the aryl mercaptans and mercaptides, the term "ary being used in its commonly accepted sense as meaning an aromatic hydrocarbon radical. By a heavy metal, I mean a metal having a density greater than 4.0. Ordinarily, the heavy metals employed for forming the aromatic mercaptides will be zinc, cadmium, nickel, tin and lead, of which zinc will usuallybe preferred.

The nickel aliphatic zanthates should be substantially neutral, that is, they should be free of strongly acidic groups and strongly basic groups. The aliphatic xanthates have the valence of oxygen in the xanthic acid residue satisfied by an aliphatic carbon of a monovalent organic radical. Preferably, the aliphatic radical is a hydrocarbon radical, but it may be a substituted hydrocarbon radical in which the substituent is substantially neutral, such as halogen. In all cases, the activity of the xanthates for the purposes of the present invention depends primarily on the presence in the molecule of the nickel atom attached to 2 xanthic acid residues, rather than upon the aliphatic group attached to the oxygen.

The quantities of the mercaptans or mercaptides and the nickel xanthates, that is, the composition and quantity of the placticizing mixture, 1 a

will be chosen according to the degree of plasticizing required, the temperature and degree of mechanical working to be employed and the type of rubber to be treated. The amount of aromatic mercaptan employed may be in the range of from about 0.003% to about 0.5% by weight, based on the rubber, and, preferably, in the proportion of from about 0.005% to about 0.15%. The amount of the nickel xanthate may be from about 0.004% to about 0.05% by weight, based on the rubber, and preferably, from about 0.001% to about 0.02%. The ratio of aromatic mercaptan or mercaptide to nickel xanthate may vary from about 0.2 to about 5000 parts of mercaptan or mercaptide to each part of nickel xanthat and, 4

preferably, from about 5 to about parts of mercaptan or mercaptide to each part of nickel x'anthate; provided that the proportions of each added to the rubber is maintained within the range above set forth.

While the mercaptan or the mercaptide and the nickel xanthate may be separately added to the rubber, it will usually be preferred to mix them to provid plasticizing compositions to be xanthate will dissolve in the mercaptan in the desired proportions to provide a stable composition which can be used as such. In other cases, simple mixtures may be used; with or without an inert solid diluent. The solid diluent may be any filler or pigment for rubber, such as clay, whiting, carbon black, talc, silica, barytes and the like. The amount of solid diluent may be any amount up to that which it is desired to have in the final rubber composition. Ordinarily, it will be desirabl to dissolve the required proportions of mercaptan or mercaptide and nickel xanthate in a substantially neutral mutual organic solvent so as to contain the plasticizing mixture in a concentration of from about 10% to about by weight in the solvent. Suitable solvents are hydrocarbons, alcohols and esters which may be aromatic, aliphatic or cycloaliphatic. Preferably, the solvent is one which is volatile under the processing conditions to be used or is a substance, such as a lubricating oil, which is commonly used in the compounding of rubber. Mixtures of 2 or more solvents may be employed and, where an aromatic mercaptide is involved, the solvent should include an alcohol. Representative solvents which may be employed are those disclosed in U. S. Patents 2,064,580, 2,378,519, 2,467,789, hereinbefore referred to, and in U. S. Patent 2,413,531.

The plasticizing agents and compositions will be incorporated in the raw rubber during the conventional peptizing and plasticizing processes. Ordinarily, such processes will be carried out in standard rubber processing equipment, such as a Gordan Plasticator, Banbury mixer, Werner- Pileiderer mixer, or on a rubber mill. The plasticizing process should be carried out at a temperature of from about 100 C. to about 200 C.

In order to more clearly illustrate my invention, prefered modes of carrying the same into efiect and the advantageous. results to be obtained thereby, the following examples are given:

EXAMPLE I 30 parts of smoked sheet rubber were placed on a small (6" x 2") rubber mill and masticated for 3 minutes at 135 C. The agents to be tested were then added in the quantity per cent by weight) indicated in the following Table l and mixed with the rubber at 135 C. for 12 minutes. The plasticized rubber so obtained was removed as a sheet and folded. Plasticity pellets were cut from a sample of the plasticized polymer and plasticity and recovery measured on a Williams parallel plate plastometer (Williams, Ind. Eng. Chem., 362, 1924), following the procedure used in Patent No. 2,467,789. Data obtained, using mixtures of xylyl mercaptan and nickel .xanthates as processing agents for rubber, are readded to the rubber. Frequently, the nickel corded in Table 1.

Table 1 WILLIAMS PLASTIGITY-RECOVERY MEASUREMENTS 1 Per- Per- Aromatic Thiol cent Promoter cent P R 1 Used Used None None 199 58 Xylyl Mcrcaptan 0. 055 do 120 7 Do 0. 182 do 1 Nickel ethyl xanthate 0.05 88 1 Nickel isoamyl xanthate 0.05 87 4 Nickel propyl xanthate 0. 05 85 2 1 As more fully explained in Patent No. 2,467,789, P is the plasticity number or thickness of the standard test pellet immediately after compression and is inversely proportional to the plasticity, and R is a measure of the recovery of the sampler after removal of the compressing lorce,

Nickelowl-matinee are. alsoefiectiv'e, promoters for aromatic. mercaptides.) Using thettesting technique. described in E xamp1eJI, an number. of nickelixanthates.wereevaluated ae promoters for the; aromatic: mercaptidem plasticization of; nat11= ra l-rubber; Thedatararevsummarized mzramez:

breakdown; of: mbbem cam be: accomplished,

compietelytamdein az: shorter tinietwiflr appreeiablersavin'gssinflabdrf amtzpower consuinp tiongand 'conseqi-iently: a mire-ii: greater oiitpiit from each piecebf 111131581 e uipment; 4 Tl'ir' HJISO'f-a saving'iH-cost-"of p esmcizmg agent; tfiermo're; the piersticizihgagents disper'se i wen It will be understood,- that the; preceding eXamF- plesware given for. illustrative: purposes. solely and that my -invention ismot to.- be: limited to; theespecific-l-embodiments disclosed therein but, that manynvariations and; modificatienamay: bemadetlfierein-v without departing from: the, spirit or scope ofrmy inventionh Examples: of: other aromatic; mercantans that are plasticizing agenteiorr rubber andtmay be used as:- suchv or as mercapticles 0f= the divalent heavy metals; in. conjunction; with nickel a1i-' phatictxan-thates: in accord With my' invention Examples of otheraromatic; mercaptide's:v that are: plasticizing: agents: forznubber and; may be used;inzconjunctiomwithr nickel; aliphatic thatesrare zinci phenyl'; mercaptidm. zimz-ornit'rophenyl: mencaptide: zinceo-hydroxyphenylx. mere captide;=. zinc:-Io.-camboxyphenyl .mereaptide, thiomrnaphthyl :7 mercaptide;-. zinc; anthryl': merrcaptide andi anthraqui'nonyl'; ,mercaptide; 'Bhapreierredimercaptideszareszinc XyIyLmercapE- tide ocadmium xylyll mercaptide: and; leadlixylyl mercaptidez. Y

. Examples: of other;sub'stantiallyneutr aLnickel aliphaticixanthates that: be: used; for; the

p i l oses of this invention areanickel v methyl xanthate; nickel isopropyl; xamha'tm. nickel benzylixanthate, nickel 2i-ch'loroethyl) xanthate andlnickel ('2;ethylhexyh':- xanthatezw Theme;- ferred compounds; are nickel. ethyls. xanthat'e, nickel isopropylii xaiithatee amf fi nickei: isoamyl xantha'te:- l

' It will be: apparent thaiglby mwinventiom the promoter offthe plasti'cizi'nga'aotioni in" rubbert, soften the" rubber; and also improvethe' processing: characteristics of" the: rubber" and the ease with which other. compounding ingredi ent's are-incorporated? Thus; it will be apparent that my, invention constitutes a valuable advance and contribution to-th'e'artr' 11 The process-for improvihg theplasticittfof rubber' whichcomprises" mixing into" the rubber. from about' 0.003% to about*0.5 77' of a rubber pl'asticizing 'a'gentof thegrou'p' con'sisting offaromati'c mercapt'an'sand aromatic mercaptides of diva-lent heavy metals ancl from about 020'004-7; to about 0. 05 of a= substantially" neutral nicke1 aliphatic Xanth'atevehicii -is a? strongpromoterof the plastici'zing mum of the plasticizing agent;

22" The proces'sfor improvingthe-plastieity of rubber which comprises;-mi-xing into"tlie--rubber from about 0-100373 to -about- 0i5*%"of a rubber plastieizing aromatic mercaptan and from about 02000476 to-about 0.05% of at substantially neutral nickel emphatic xanthate which": i's a strong thee-men?- captamv 3o The; process for? improving; the plasticity of rubber which comprises mixingdnto the rubber fromiabout'r 03003985 to: abouttflfl *ofixylfl merc'aptan: and fromabout 0:0004 to about: 0.055% of a substantially neutrali nickel aliphatic; xair thatewhichsisra strong: promoter, of theiplastife cizingsaotien'lof the'smercaptan. 1

4i The processrfcirrimproving the plasticity of rubber which comprises: mixing intchthea'nubbei: from: about? 050.03%. to: about; 0:57;; a;- rubber p1asticizing?" aromatic; mercaptide on at, divalent heavy 'meta'lv andv fromzabouti 020004678; to about (L05 5%: otlai; substantially; neutral; nicieel; aliphatic xanthate which Lissa;strongmrnmotetofitheiplaseticizing action of the mercaptide:

5;; Th'fii process: fon'iinpmving' gthez plasticity? of rubber: whiclricomprises; mixing; into the: rubber from; about: 030039211: to: about; 0.5%; :QfrZiflc: xylyl mercaptider and-:. from: aboum 031001162 to about 015%: of: a, substantially neutral-nickel al-ighatic .xzmthazte iwhidhiis asstrongg promotenofrth'erplase ticizingia-ctlomofthe mercagtide;v I a 6'2 Theepnocesssforrimproving: thepl'asticityfiof 'mbherrwhichz comprises: mixingsintathe;-:1:ubber from about 0.0003%'to about 0.5% of a rubber plasticizing agent of the group consisting of aromatic mercaptans and aromatic mercaptides of divalent heavy metals and from about 0.0004% to about 0.05% of a neutral nickel aliphatic Xanthate which, except for the'nickel and the oxygen and sulfur. of the xanthic acid group, consists of carbon and hydrogen and which xanthate is a strong promoter of the plasticizing action of the plasticlzing agent.

7. The process for improving the plasticity of rubber which comprises mixing into the rubber from about 0.003% to about 0.5% of a rubber plasticlzing aromatic mercaptan and from about 0.0004% to about 0.05% of a neutral nickel aliphatic xanthate which, except for the nickel and the oxygen and sulfur of the xanthic acid group, consists of carbon and hydrogen and which xanthate is a strong promoter of the plasticlzing action of the mercaptan.

8. The process for improving the plasticity of rubber which comprises mixing into the rubber from about 0.008% to about 0.5% of a rubber plasticlzing aromatic mercaptide of a divalent heavy metal and from about 0.0004% to about 0.05% of a neutral nickel aliphatic xanthate which, except for the nickel and the oxygen and sulfur of the xanthic acid group, consists of carbon and hydrogen and which xanthate is a strong promoter of the plasticizing action of the mercaptide.

9. A composition, suitable for plasticlzing rubber, which comprises essentially from about 1 to about 50 parts of a rubber plasticizing agent of the group consisting of aromatic mercaptans and aromatic mercaptides of divalent heavy metals and 1 part of a substantial neutral nickel aliphatic xanthate which is a strong promoter of the plasticizing action of the plasticizing agent.

10. A composition, suitable for plasticlzing rubber, which comprises essentially from about 1 to about 50 parts of a rubber plasticizing aromatic mercaptan and 1 part of a substantially neutral nickel aliphatic xanthate which is a strong proaction of the mercapa substantially neutral nickel aliphatic xanthate which is a strong promoter of the plasticlzing action of the mercaptan.

12. A composition, suitable for plasticlzing rubber, which comprises essentially from about 1 to about 50 parts of a rubber plasticizing aromatic mercaptide of a divalent heavy metal and 1 part of a substantially neutral nickel aliphatic xanthate which is a strong promoter of the plasticizing action of the mercaptide.

' 13. A composition, suitable for plasticlzing rubber, which comprises essentially from about 1 to about 50 parts of zinc xylyl mercaptide and 1 part of a substantially neutral nickel aliphatic xanthate which is a strong promoter of the plasticizing action of the mercaptide.

' 14. A composition, suitable for plasticizing rubher, which comprises essentially from about 1 to about 50 parts of a rubber plasticlzing agent of the group consisting of aromatic mercaptans and aromatic mercaptides of divalent heavy metals and 1 part of a neutral nickel aliphatic xanthate which, except for the nickel and the oxygen and. sulfur of thexanthic acid group, consists of carbon and hydrogen and which xanthate is a strong promoter of the plasticizing action of the plasticlzing agent.

15. A composition, suitable for plasticizing rub her, which comprises essentially from about 1 to about 50 parts of a rubber plasticizing agent of the group consisting of aromatic mercaptans and aromatic mercaptides of divalent heavy metals and 1 part ofa substantially neutral nickel aliphatic xanthate which is a strong promoter of the plasticlzing action of the plasticizing agent, dissolved in a concentration of from about 10% to about 50% by weight in a substantially neutral mutual organic solvent of at least one member of the class consisting of hydrocarbons, alcohols and esters.

16. A composition, suitable for plasticlzing rubber, which comprises essentially from about 1 to about 50 parts of a rubber plasticizing aromatic mercaptan and 1 part of a substantially neutral nickel aliphatic xanthate which is a strong promoter of the plasticizing action of the mercaptan, dissolved in a concentration of from about 10% to about 50% by weight in a substantially neutral mutual organicsolvent of at least one member of the class consisting of hydrocarbons, alcohols and esters.

' 17. A composition, suitable for plasticlzing rubber, which comprises essentially from about 1 to about 50 parts of xylyl mercaptan and 1 part of a substantially neutral nickel aliphatic xanthate which is a strong promoter of the plasticizing action of the mercaptan, dissolved in a concentration of from about 10% to about 50% by weight in a substantially neutral mutual organic solvent of at least one member of the class consisting of hydrocarbons, alcohols and esters.

13. A composition, suitable for plasticizing rubber, which comprises essentially from about 1 to about 50 parts of a rubber plasticlzing aromatic mercaptide of a divalent heavy metal and 1 part of a substantially neutral nickel aliphatic xanthate which is a strong promoter of the plasticlzing action of the mercaptide, dissolved in a concentration of from about 10% to about 50% by weight in a substantially neutral mutual organic solvent of at least one member of the class consisting of hydrocarbons, alcohols and esters.

19. A composition, suitable for plasticizing rubber, which comprises essentially from about 1 to about 50 parts of zinc xylyl mercaptide and 1 part of a substantially neutral nickel aliphatic xanthate which is a strong promoter of the plasticizing action of the mercaptide, dissolved in a concentration of from about 10% to about 50% by weight in a substantially neutral mutual organic solvent of at least one member of the class consisting of hydrocarbons, alcohols and esters.

20. A composition, suitable for plasticizing rubber,'which comprises essentially from about 1 to about 50 parts of a rubber plasticlzing agent of the group consisting of aromatic mercaptans and aromatic mercaptides of divalent heavy metals and 1 part of a neutral nickel aliphatic xanthate which, except for the nickel and the oxygen and sulfur of the xanthic acid group, consists of carbon and hydrogen and which xanthate is a strong promoter of the plasticlzing action of the plasticizing agent, dissolved in a concentration of from about 10% to about 50% by weight in a substantially neutral mutual organic solvent of at least one member of the class consisting'of hydrocarbons, alcohols and esters.

21. A composition, suitable for plasticizing rubber, which comprises essentially from about 1 to about 50' parts of a rubber plasticlzing agent of the group consisting of aromatic mercaptans and aromatic mercaptides of divalent heavy metals and 1 part of neutral nickel isopropyl xanthate which is a strong promoter of the plasticizing action of the plasticizing agent.

22. A composition, suitable for plasticizing rubher, which comprises essentially from about 1 to about 50 parts of a rubber plasticizing agent of the group consisting of aromatic mercaptans and aromatic mercaptides of divalent heavy metals and 1 part of neutral nickel ethyl xanthate which is a strong promoter of the plasticizing action of the plasticizing agent.

23. A composition, suitable for plasticizing rubher, which comprises essentially from about 1 to about 50 parts of a rubber plasticizing agent of the group consisting of aromatic mercaptans and aromatic mercaptides of divalent heavy metals and 1 part of neutral nickel isoamyl xanthate which is a strong promoter of the plasticizing action of the plasticizing agent.

JOHN J. VERBANC.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. THE PROCESS FOR IMPROVING THE PLASTICITY OF RUBBER WHICH COMPRISES MIXING INTO THE RUBBER FROM ABOUT 0.003% TO ABOUT 0.5% OF A RUBBER PLASTICIZING AGENT OF THE GROUP CONSISTING OF AROMATIC MERCAPTANS AND AROMATIC MERCAPTIDES OF DIVALENT HEAVY METALS AND FROM ABOUT 0.0004% TO ABOUT 0.05% OF A SUBSTANTIALLY NEUTRAL NICKEL ALIPHATIC XANTHATE WHICH IS A STRONG PROMOTER OF THE PLASTICIZING ACTION OF THE PLASTICIZING AGENT. 